Greenhouses made of flexible sheet material, such as transparent polyethylene sheet, have come into widespread use. The greenhouses are made by constructing structural elements such as spaced columns connected with metal arches and then stretching transparent or translucent flexible sheet material over the structure. In a preferred structure two sheets of flexible sheet material are provided and air under pressure is injected between them whereby the two sheets are held apart by the inflating air. Such structure requires that the two sheets be held together at their edges in a sealing relationship so that the inflating air cannot escape too rapidly.
To provide a sealing relationship at the edges of double-sheet structures, elongated clamps have been developed. These clamps generally have means that lock the edges of the flexible sheets together with adequate force to seal the air between them but with not enough force to tear or destroy the sheets. Preferably the locks are releasable so that the sheets can be removed or replaced. The devices for locking the sheets together and holding them in place are usually connected to the greenhouse structure, for example, adjacent to the roof portion or if several structures are employed side by side in the gutter areas between them.
Several locking devices are commercially available. The better of these include an elongated cavity into which the edge portions of the polyethylene sheets are placed after which a locking element is inserted into the cavity thereby pressing the double sheets against the interior wall of the cavity and holding them in place. The other end of the locking element is then restrained with a separate clip. Problems with the prior products of this type are that separate clips are needed which require tools to install, the clips are frequently sharp or in any event interfere with those portions of the flexible sheet material that extend beyond them, and the sheet material must be cut to provide space for the clips to engage the locking devices.